Antenna Trajectory-Aware Mechanical Fluid Antenna-Enhanced Secure Wireless Communications

This paper investigates the impact of mechanical fluid antenna (FA) trajectory on enhancing secure wireless communication, aiming to mitigate the effects of delays caused by antenna movement. To achieve this, we jointly optimize the FA trajectory and transmit beamformer to maximize the secrecy rate. For any given trajectory, we derive the optimal transmit beamformer. Additionally, we study two typical scenarios: continuous trajectory and discrete trajectory. In the continuous trajectory design, we reformulate the time-averaged secrecy rate maximization problem into a mean squared error (MSE) minimization problem and employ the block successive upper bound minimization (BSUM) algorithm for optimization. For the discrete trajectory, we express the beamformer as a function of the FA trajectory which means the secrecy rate only depends on the FA trajectory. Then we apply successive refinement to iteratively optimize the FA position in each time slot. Numerical results demonstrate that our trajectory-aware FA design significantly enhances secure wireless communication, particularly under varying power budgets and antenna speeds.